Miniature electron or ion beam columns offer many advantages over conventionally built electron or ion columns in terms of simplicity, footprint, and cost. Scaling the electron optical components of electrostatic lens systems reduces lens aberrations roughly linearly with scale factor resulting in spot-size and beam current comparable to high-end conventional magnetic lenses. Challenges in fabrication have been mostly overcome by careful engineering and deep silicon etching techniques which meet or exceed circularity and sidewall roughness tolerances. Likewise, column alignment, especially lens-to-lens or lens-to-limiting aperture requirements can be met by suitably placed registration marks and new generations of pick-and-place tools.
A remaining difficulty with miniature columns, however, is the physical alignment of the electron/ion source optical axis to the extraction electrode, the limiting aperture and other column elements. Unlike conventional systems, in which the bore diameter of the extractor and the distance from source to extractor is substantially larger than the mechanical alignment tolerance of the source, miniature columns require alignment accuracy on the micron scale. Even thermal-induced motion of the tip from normal heating during operation can cause shifts that significantly degrade performance or prevent column operation altogether. Previous solutions have relied on in-situ mechanical alignment of the tip with a two or more axis ultra-high vacuum compatible stage or flexure. While successful in some circumstances, this approach is expensive, unreliable, and bulky.
Accordingly, a new apparatus and method are needed for alignment of charged particle beams.